Compressors for refrigeration are generally provided with a discharge muffler. Such muffler has the purpose of attenuating the pulsation of the gases which are pumped from the compressor to the refrigeration system, or generally, to the high-pressure side of the circuit to which the compressor belongs, as well as reducing the noise irradiated by the compressor to the external ambient. The pulsation of the gases generates an excitation in the ducts and components to which the discharge of the compressor is coupled, leading to the always undesired generation of noise. Several configurations are used for said muffler, but in general the principle is to make the gas flow pass through a well defined sequence of tubes, volumes and localized restrictions, whose dimensions, arrangement and specific characteristics depend on the application, on the type and size of the compressor, on the mass flow, on the working fluid, on the temperatures and operating conditions, on the noise bands which are intended to attenuate, etc.
The following facts are relevant to understand the phenomena involved in the operation of the object of this description:                Before starting the operation, the compressor is generally submitted to a null or reduced pressure differential between the suction and the discharge. This common pressure is called equalizing pressure and its value is a direct function of the project characteristics of the system, of the type of refrigerant fluid and lubricant fluid that are used, and of the temperatures to which the refrigeration system is submitted. Since there is not a relevant pressure differential between the suction and discharge, the mass flow which is established in the initial instants of the compressor operation is always very high, usually one order of magnitude above the mass flow in a normal operating regime. The higher the density of the working fluid, the higher the value of the mass flow, i.e., the greater the value of the equalized pressure and the lower the fluid temperature, the greater the value of the mass flow.        Even in systems in which devices are provided to maintain the pressure differential, with the compressor being in a stop condition, the mass flow is naturally greater during the compressor start;        The tubes and localized restrictions existing in the discharge muffler cause load loss to the working fluid flow, whose variation is, in a first approach, linear with the mass flow;        The power required from the motor of the compressor is the sum of the powers required to overcome the friction forces which appear upon the movement of the driving mechanism plus the powers which are necessary to compress and pump the gas. This last power part corresponds, in a no-load starting condition, to the flow load loss. In a normal operating condition, the mass flow is such that the power needed to pump the gas is low, as compared to the other parts. However, in a starting condition, the power dissipated for pumping the gas is much greater than the other power parts.        The compressor components are, as a rule, designed to give maximum efficiency when said compressor operates in the normal operating regime. In the case of the motor, there is a negative correlation between the maximum available power and maximum efficiency. The same is true to the maximum available power and motor cost. Thus, it is always interesting to reduce at maximum the requirement for maximum motor power, which is correlated with operating conditions with high mass flow or, as a rule, upon the compressor start.        
In view of the facts exposed above, there is a compromise relationship between the project of the motor and the project of the discharge muffler. The latter implies, intrinsically, a restriction to the gas flow (load loss), which restriction increases as the mass flow increases. If this load loss is reduced, the maximum power required from the motor will be less strict, which means a project with the possibility of obtaining higher efficiencies and/or lower costs.
FIGS. 1 and 2 show, schematically, two other known prior art constructions for the discharge muffler, one of them (FIG. 1) presenting a solution for a discharge muffler arranged “in series”, and the other construction (FIG. 2) presenting a solution for a muffler arranged “in parallel”.
The solution of the discharge system with the arrangement “in series” presents the disadvantage of having higher load loss but higher attenuation, whereas the solution with the arrangement in parallel presents lower restriction to the flow between the volume of the cylinder cover and the volumes of the muffler, but lower noise attenuation.